Thirty-one pro-Russian separatists were reportedly killed in a fire during clashes between rival groups in the southern port city. At least three Ukraine service men have been killed in skirmishes in Sloviansk.

Officials in Kiev are claiming that Moscow is preparing an invasion force tens of thousands strong on the frontier with Ukraine and that "Russian sabotuers" are sowing the seeds of unrest in the east to ease the way.

The Kremlin has deined these allegations, but the Russian foreign minister Sergei Lavrov has warned that his country would respond to attacks on their citizens or interests in Ukraine. Vladmir Putin's spokesman said that the Ukrainian offensive had "effectively destroyed the last hope for the implementation of the Geneva agreement."

A protester throws a petrol bomb at the trade union building in Odessa. Credit: Reuters\Yevgeny Volokin

Unlike the rest of the country, the port city of Odessa in the south had been largely untouched by violence until today but clashes today between pro-Russian separatists and activists loyal to the government in Kiev left at least 38 dead, according to local police and security forces